Method for manufacturing an elastomeric composition having a self-sealing property

ABSTRACT

Process for the manufacture of an elastomer composition having a self-sealing property which is based on at least (phr meaning parts by weight per 100 parts of solid elastomer): a solid unsaturated diene elastomer; between 30 and 90 phr of a hydrocarbon resin; from 0 to less than 30 phr of filler; between 0.5 and 15 phr of thiuram polysulphide, in which, during a first stage or stage (a), a masterbatch comprising at least the solid unsaturated diene elastomer and between 30 and 90 phr of a hydrocarbon resin is prepared by mixing these various components in a mixer at a “hot compounding” temperature or up to a “hot compounding” temperature which is greater than the softening temperature of the hydrocarbon resin.

RELATED APPLICATIONS

This is a U.S. national stage of application No. PCT/EP2011/050859,filed on Jan. 21, 2011. Priority is claimed on the followingapplication: French Application No. 1050598 filed on Jan. 28, 2010, thecontent of which is hereby incorporated here by reference.

FIELD OF THE INVENTION

The present invention relates to self-sealing compositions which can beused as puncture-resistant layers in any type of “inflatable” article,that is to say, by definition, any article which takes its usable shapewhen it is inflated with air.

It relates more particularly to processes for the manufacture ofself-sealing compositions based on a diene elastomer, such as naturalrubber.

BACKGROUND OF THE INVENTION

For some years, tire manufacturers have been making particularly greatefforts to develop novel solutions to a problem dating from the verybeginning of the use of wheels fitted with tires of inflated type,namely how to allow the vehicle to continue its journey despite asignificant or complete loss of pressure from one or more tires. Fordecades, the spare wheel was regarded as the sole and universalsolution. Then, more recently, the considerable advantages related toits possible removal have become apparent. The concept of “extendedmobility” was developed. The associated techniques make it possible torun with the same tire, according to certain limits to be observed,after a puncture or a fall in pressure. This makes it possible, forexample, to drive to a breakdown point without having to halt, underoften hazardous conditions, to fit the spare wheel.

Self-sealing compositions capable of making it possible to achieve suchan objective, by definition capable of automatically ensuring, that isto say without any external intervention, the airtightness of a tire inthe event of perforation of the latter by a foreign body, such as anail, are particularly difficult to develop.

In order to be able to be used, a self-sealing layer has to satisfynumerous conditions of a physical and chemical nature. In particular, ithas to be effective over a very wide range of operating temperatures,this being the case over the whole of the lifetime of the tires. It hasto be capable of sealing the hole when the perforating article remainsin place; when the latter is expelled, it has to be able to fill in thehole and to render the tire airtight.

Numerous solutions have admittedly been devised but they have not beenable truly to be developed to date in vehicle tires, particularly due todifficulties in manufacturing these self-sealing compositions and thusto their final cost price.

In particular, high-performance self-sealing compositions based onnatural rubber and hydrocarbon resin as tackifying agent (tackifier)have been described in Patents U.S. Pat. No. 4,913,209, U.S. Pat. No.5,085,942 and U.S. Pat. No. 5,295,525. These compositions arecharacterized by the combined presence of a high content of hydrocarbonresin, always greater than 100 parts by weight per hundred parts ofsolid elastomer, and of a large amount of elastomer in the liquid state,generally in the form of depolymerized natural rubber (molecular weighttypically of between 1000 and 100 000).

First of all, such a high resin content, apart from the fact that it canbe harmful to the hysteresis and consequently to the rolling resistanceof the tires, requires a particularly lengthy and difficult kneading ofthe elastomer matrix.

The use of a large amount of liquid elastomer admittedly improves thefluidity of the composition but such a use is the source of otherdisadvantages, in particular of a risk of creep of the self-sealingcomposition during use at relatively high temperature (typically greaterthan 60° C.) frequently encountered during the use of some tires.

Another major manufacturing problem may also arise: in the absence offiller, such as carbon black, or at the very least of a significantamount of such a filler (furthermore undesirable, in a known way, forthis type of application), the composition exhibits weak cohesion. Thislack of cohesion may be such that the adhesiveness of the composition,resulting from the high content of tackifying resin employed, is nolonger compensated for and prevails. This then results in a risk ofundesirable adhesive bonding to the compounding equipment, which isunacceptable under industrial processing conditions.

SUMMARY OF THE INVENTION

One object of the invention is to provide a novel manufacturing processwhich makes it possible to palliate, at the very least to significantlyreduce, the various abovementioned disadvantages.

To attain this and other objects, one aspect of the present inventionrelates to a process for the manufacture of an elastomer compositionhaving a self-sealing property which is based on at least (phr meaningparts by weight per 100 parts of solid elastomer):

-   -   a solid unsaturated diene elastomer;    -   between 30 and 90 phr of a hydrocarbon resin;    -   from 0 to less than 30 phr of filler;    -   between 0.5 and 15 phr of thiuram polysulphide,        in which, during a first stage or stage (a), a masterbatch        comprising at least the solid unsaturated diene elastomer and        between 30 and 90 phr of a hydrocarbon resin is prepared by        mixing these various components in a mixer at a “hot        compounding” temperature or up to a “hot compounding”        temperature which is greater than the softening temperature of        the hydrocarbon resin.

Such a process has proved to be particularly well suited to the rapidmanufacture, under processing conditions acceptable from the industrialviewpoint, of a high-performance self-sealing composition based on soliddiene elastomer and on hydrocarbon resin, it being possible for thiscomposition to comprise high contents of hydrocarbon resin withoutrequiring the use of elastomer in the liquid state as plasticizer.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its advantages will be easily understood in the lightof the description and implementational examples which follow, and ofFIGS. 1 and 2 relating to these examples, which give a simplediagrammatic representation, without observing a specific scale:

FIG. 1 shows an example of an extrusion-compounding device which can beused for the implementation of a process in accordance with theinvention; and

FIG. 2 shows in radial cross section, an example of a tire using aself-sealing composition prepared according to the process in accordancewith the invention.

I. DETAILED DESCRIPTION

I-1. Definitions

In the present description, unless expressly indicated otherwise, allthe percentages (%) indicated are % by weight.

Furthermore, any interval of values denoted by the expression “between aand b” represents the range of values greater than “a” and lower than“b” (that is to say, limits a and b excluded), whereas any interval ofvalues denoted by the expression “from a to b” means the range of valuesranging from “a” up to “b” (that is to say, including the strict limitsa and b).

The abbreviation “phr” means parts by weight per hundred parts ofelastomer in the solid state (of the total of the solid elastomers, ifseveral solid elastomers are present).

The expression composition “based on” should be understood as meaning,generally, a composition comprising the mixture and/or the reactionproduct of its various components, it being possible for some of thesecomponents to be capable of reacting (indeed even intended to react)with one another, at least in part, during the various phases ofmanufacture of the composition, in particular during its finalcrosslinking or vulcanization (curing).

Elastomer (or “rubber”, the two being regarded as synonyms) of the“diene” type should be understood as meaning, in a known way, anelastomer resulting at least in part (i.e., a homopolymer or acopolymer) from diene monomers (i.e., from monomers carrying twocarbon-carbon double bonds, whether conjugated or nonconjugated).

These diene elastomers can be classified into two categories, saturatedor unsaturated. In the present patent application, “unsaturated” dieneelastomer is understood to mean a diene elastomer resulting at least inpart from conjugated diene monomers and having a content of unitsresulting from conjugated dienes which is greater than 30% (mol %). Thusit is that diene elastomers such as butyl rubbers or copolymers ofdienes and of α-olefins of EPDM type, which can be described as“saturated” diene elastomers due to their reduced content of units ofdiene origin (always less than 15 mol %), are excluded from thepreceding definition. The commonest diene elastomers of the unsaturatedtype are those selected from the group consisting of polybutadienes,natural rubber, synthetic polyisoprenes, butadiene copolymers, isoprenecopolymers and the mixtures of such elastomers.

I-2. Measurements

I-2-A. Mooney Viscosity

The Mooney viscosity or plasticity characterizes, in a known way, solidsubstances. Use is made of an oscillating consistometer as described inStandard ASTM D1646 (1999). The Mooney plasticity measurement is carriedout according to the following principle: the sample, analysed in theraw state (i.e., before curing), is moulded (formed) in a cylindricalchamber heated to a given temperature (for example 35° C. or 100° C.).After preheating for one minute, the rotor rotates within the testspecimen at 2 revolutions/minute and the working torque for maintainingthis movement is measured after rotating for 4 minutes. The Mooneyviscosity (ML 1+4) is expressed in “Mooney unit” (MU, with 1 MU=0.83newton.metre).

I-2-B. Brookfield Viscosity

The Brookfield viscosity characterizes, in a known way, liquidsubstances. The apparent viscosity according to the Brookfield method ismeasured at a given temperature (for example at 65° C.) according toEuropean and International Standard EN ISO 2555 (1999). Use is made, forexample, of a viscometer of the A type (for example RVT model) or of theB type (for example HAT model) at a rotational frequency preferablyequal to 10 or 20 min⁻¹, with a No. of the spindle (1 to 7) suitable forthe viscosity range measured (according to Appendix A of Standard EN ISO2555).

I-2-C. Macrostructure of the Elastomers

The macrostructure (Mw, Mn and PI) and the distribution of the molarmasses of an elastomer, whether in the liquid state or in the solidstate, are characteristics known to a person skilled in the art,available in particular from the suppliers of elastomers, which canfurthermore be measured by conventional techniques, such as GPC (GelPermeation Chromatography) or SEC (Size Exclusion Chromatography).

To recapitulate, the SEC analysis, for example, consists in separatingthe macromolecules in solution according to their size through columnsfilled with a porous gel; the molecules are separated according to theirhydrodynamic volume, the bulkiest being eluted first. The sample to beanalysed is simply dissolved beforehand in an appropriate solvent, forexample tetrahydrofuran, at a concentration of 1 g/litre. The solutionis then filtered through a filter, for example with a porosity of 0.45μm, before injection into the apparatus. The apparatus used is, forexample, a “Waters Alliance” chromatographic line. The elution solventis, for example, tetrahydrofuran, the flow rate is 0.7 ml/min and thetemperature of the system is 35° C. set of 4 “Waters” columns in series(names “Styragel HMW7”, “Styragel HMW6E” and two “Styragel HT6E”) is,for example, used. The injected volume of the solution of the polymersample is, for example, 100 μl. The detector is a differentialrefractometer (for example “Waters 2410”) which can be equipped withassociated software for making use of the data (for example “WatersMillennium”). A Moore calibration is carried out with a series ofcommercial polystirene standards having a low PI (less than 1.2), withknown molar masses, covering the range of masses to be analysed. Theweight-average molar mass (Mw), the number-average molar mass (Mn) andthe polydispersity index (PI=Mw/Mn) are deduced from the data recorded(curve of distribution by mass of the molar masses).

I-2-D. Macrostructure of the Hydrocarbon Resins

The macrostructure (Mw, Mn and PI) is determined by SEC as indicatedabove for the elastomers: solvent tetrahydrofuran, temperature 35° C.,concentration 1 g/litre, flow rate 1 ml/min, solution filtered through afilter with a porosity of 0.45 μm before injection (100 μl); Moorecalibration with polystirene standards; set of 3 “Waters” columns inseries (“Styragel HR4E”, “Styragel HR1” and “Styragel HR 0.5”),detection by differential refractometer (for example “Waters 2410”)which can be equipped with operating software (for example “WatersMillennium”).

All the values for molar masses shown in the present application arethus relative to calibration curves produced with polystirene standards.All the values for glass transition temperature (“Tg”) are measured in aknown way by DSC (Differential Scanning calorimetry) according toStandard ASTM D3418 (1999).

I-3. Process of the Invention

The process in accordance with the invention thus has the essentialcharacteristic of comprising a first stage or stage (a) during which amasterbatch comprising at least the solid unsaturated diene elastomerand between 30 and 90 phr of a hydrocarbon resin is prepared by mixingthese various components in a mixer at a “hot compounding” temperatureor up to a “hot compounding” temperature which is greater than thesoftening temperature of the hydrocarbon resin.

The hot compounding temperature above is, of course, that of themasterbatch measurable in situ and not the set temperature of the mixeritself.

“Masterbatch” or “intermediate composition” should be understood asmeaning the mixture of at least the solid diene elastomer with thehydrocarbon resin, the precursor mixture of the final ready-for-useself-sealing composition. Various additives can optionally beincorporated in this masterbatch, whether they are intended for themasterbatch proper (for example, a stabilizing agent, a colouring agent,a UV stabilizer, an antioxidant, and the like) or for the finalself-sealing composition for which the masterbatch is intended.

The masterbatch can be manufactured in any compounding equipment, inparticular in a blade mixer, an open mill, an extruding machine or anymixer capable of sufficiently mixing or kneading its various componentsuntil a homogeneous intimate mixture of the said components is obtained.Preferably, use is made of a compounding screw extruder, having or nothaving a constant pitch, capable in a known way of introducingsignificant shearing of the mixture (diene elastomer and resin) beingformed.

In the initial state, that is to say before contact thereof with thesolid elastomer, the hydrocarbon resin can exist in the solid state orthe liquid state. During the operation in which the solid elastomer andhydrocarbon resin are brought into contact, the hydrocarbon resin can bein the solid state or, according to a more preferred embodiment, alreadyin the liquid state; it is sufficient for this to heat the resin to atemperature greater than its softening temperature.

According to the type of hydrocarbon resin used, the maximum hotcompounding temperature is preferably greater than 70° C., preferablygreater than 80° C., for example between 100° C. and 150° C.

For optimum compounding of the masterbatch, the hydrocarbon resin ispreferably injected in the liquid state, under pressure, into the mixer.According to another preferred embodiment, in combination or not incombination with the above, the hot compounding stage (a) is carried outwith the exclusion of oxygen. The injection of the resin under pressure,at a temperature at which the resin is completely molten, has theadvantage of introducing, into the compounding chamber of the mixer, adegassed resin which is more stable mechanically and chemically.

According to a preferred embodiment, the process of the inventioncomprises at least one stage (b) subsequent to stage (a) during whichthiuram polysulphide, preferably in its entirety or at least 50% byweight, is incorporated in the masterbatch thus prepared, everythingbeing mixed in the same mixer or in a different mixer.

This stage (b) of incorporation of all or part of the thiurampolysulphide can be carried out on the same mixer as that of the stage(a) which precedes, preferably a compounding screw extruder, or else onanother type of mixer, for example another compounding screw extruder oran external mixer of the two-roll open mill type.

According to a preferred embodiment, in particular when an externalmixer of the two-roll open mill type is used, stage (b) is carried outat a maximum temperature or up to a maximum temperature which is keptlower than the softening temperature of the resin, in order to limit therisks of excessive undesirable adhesive bonding of the masterbatch tothe compounding equipment. Thus, according to the type of hydrocarbonresin used, the compounding temperature of stage (b) can preferably beless than 50° C., more preferably between 20° C. and 40° C.

According to another specific embodiment, independently of the softeningtemperature of the resin, this being the case whatever the compoundingequipment used for stage (b), the latter is carried out at a maximumtemperature or up to a maximum temperature which is kept lower than 130°C., preferably lower than 100° C., in particular lower than 80° C.

If need be, an intermediate stage of cooling the masterbatch can beinserted between stages (a) and (b) described above, in order to bringits temperature to the value desired before beginning stage (b), whethera targeted temperature lower than the softening temperature of the resinor, independently, a targeted temperature lower than 130° C., preferablylower than 100° C., in particular lower than 80° C., this beforeintroduction (stage (b)) of the thiuram polysulphide into themasterbatch manufactured previously.

When a filler, such as carbon black, is used, it can be introducedduring stage (a), that is to say at the same time as the solidunsaturated diene elastomer and the hydrocarbon resin, or else during astage subsequent to stage (a), preferably during the stage (b) ofincorporation of all or part of the thiuram polysulphide. It has beenfound that a very small proportion of carbon black, preferably between0.5 and 2 phr, further improved the compounding and the manufacture ofthe composition, and its final extrudability.

The process described above makes it possible to prepare a compositioncapable of fulfilling an effective puncture-resistant role with regardto the inflation articles in which it is used in particular, it does notrequire the addition of a liquid plasticizer, such as a liquidelastomer, which can be harmful, as has already been said in theintroduction to the present statement, when such a plasticizer is usedin a large amount, to the fluidity properties and thus can result inrisks of excessive creep or the composition when used at a relativelyhigh temperature.

However, according to a specific embodiment of the invention, it can beof use in some cases, according to the specific application targeted, toadd a stage of incorporation of a liquid plasticizer (liquid at 23° C.),referred to as “low Tg” plasticizer, preferably in a small amount(content of less than 60 phr), the role of which is in particular tosoften the self sealing composition by diluting the diene elastomermatrix and the hydrocarbon resin, which can improve in particular the“cold” self-sealing performance (that is to say, typically for atemperature of less than 0° C.); its Tg is by definition less than −20°C. and is preferably less than −40° C.

The optional liquid plasticizer can be incorporated at any time, in allor part, during any one of the stages of the process of the invention,in particular during the stage (a) of manufacture of the masterbatchitself (in this case, before, during or after the incorporation of thehydrocarbon resin in the diene elastomer), “hot” (that is to say, at atemperature greater than the softening temperature of the resin) or at alower temperature, or, for example, after the manufacture of themasterbatch (in this case, before, during or after addition of all orpart of the thiuram polysulphide, indeed even during the final forming(extrusion) of the composition).

According to a specific embodiment, the liquid plasticizer isintroduced, for example, at least in part, during the stage (a) ofmanufacture of the masterbatch, more preferably in this case either atthe same time as the hydrocarbon resin or after introducing the latter.According to an advantageous embodiment, a mixture of the hydrocarbonresin and of the liquid plasticizer can be prepared prior to theincorporation in the solid diene elastomer matrix.

According to another specific embodiment, the liquid plasticizer isintroduced, for example, at least in part, during the stage (b) ofincorporation of the crosslinking agent.

According to another specific embodiment, the liquid plasticizer can beincorporated, in all or part, during a stage (c) subsequent to stage(b), that is to say after incorporation of the crosslinking agent, inthe same mixer or a different mixer from that of stage (b), whether, forexample, a compounding screw extruder or an external mixer of thetwo-roll open mill type. This incorporation is possible on the sameexternal mixer but it can be advantageous to use a compounding screwextruder into which first the mixture resulting from stage (b) and thenthe liquid plasticizer are introduced, such a compounding screw extruderbeing equipped with a zone in which strong shearing is applied and thusmaking possible good homogenization of the final self-sealingcomposition.

According to another specific embodiment, if not all of the crosslinkingagent is introduced during stage (b), then the remainder of thiscrosslinking agent can be introduced in stage (a) or in the additionalstage (c) described above.

It is also possible to successively carry out all the stages ofmanufacture of the self-sealing composition with just one device, acompounding screw extruder equipped with means for introducing andmetering the various constituents positioned in offset fashion along thecompounding chamber, with appropriate homogenization zones and with adie suited to the semi-finished. This makes it possible to carry out,with one and the same device, all the stages of preparation of theself-sealing composition.

On exiting from stage (b) or optionally from stage (c) described above,the final self-sealing composition is completed; it is formeddimensionally in a way known per se, for example by extrusion through adie with dimensions suited to the semi-finished product chosen, forexample in the form of a relatively wide rubber layer, a narrow strip ora profiled element capable of being directly used in the assembling of atire blank or also a strip which can be reused subsequently in anextrusion device.

I-4. Formulation of the Composition Having a Self-Sealing Property

The self-sealing composition or material capable of being preparedaccording to the process of the invention is thus an elastomercomposition comprising at least one solid unsaturated diene elastomer,preferably as sole or predominant elastomer, between 30 and 90 phr of, aplasticizing hydrocarbon resin and between 0.5 and 15 phr of thiurampolysulphide; in addition to various optional additives, it may or maynot comprise a small fraction (less than 30 phr) of optional filler. Itsformulation is described in more detail below.

a) Diene Elastomer

“Unsaturated diene elastomer” should be understood as meaning, ofcourse, just one unsaturated diene elastomer or a mixture of unsaturateddiene elastomers.

Use is preferably made of a diene elastomer selected from the groupconsisting of polybutadienes (BRs), natural rubber (NR), syntheticpolyisoprenes (IRs), butadiene copolymers (for example butadiene-stirenecopolymers or SBR), isoprene copolymers (other than butyl rubber) andthe mixtures of such elastomers. More preferably, this unsaturated dieneelastomer of the composition of the invention is a diene elastomerselected from the group consisting of polybutadienes (BRs), naturalrubber (NR), synthetic polyisoprenes (IRs), butadiene copolymers and themixtures of such elastomers.

Mention may in particular be made, as polybutadienes, of those having acontent of 1,2-units of between 4 and 80% or those having acis-1,4-content of greater than 80%. Mention may in particular be made,as butadiene copolymers, of butadiene-stirene copolymers (SBRs),butadiene-isoprene copolymers (BIRs) or stirene-butadiene-isoprenecopolymers (SBIRs). SBR copolymers having a stirene content of between 5and 50% by weight and more particularly between 20 and 40% by weight, acontent of 1,2-bonds of the butadiene part of between 4 and 65% and acontent of trans-1,4-bonds of between 20 and 80%, 131R copolymers havingan isoprene content of between 5 and 90% by weight and a Tg of −40° C.to −80° C., SBIR copolymers having a stirene content of between 5 and50% by weight and more particularly of between 10 and 40% by weight, anisoprene content of between 15 and 60% by weight and more particularlybetween 20 and 50% by weight, a butadiene content of between 5 and 50%by weight and more particularly of between 20 and 40% by weight, acontent of 1,2-units of the butadiene part of between 4 and 85%, acontent of trans-1,4-units of the butadiene part of between 6 and 80%, acontent of 1,2-plus 3,4-units of the isoprene part of between 5 and 70%and a content of trans-1,4-units of the isoprene part of between 10 and50%, and more generally any SBIR copolymer having a Tg of between −20°C. and −70° C., are suitable in particular.

According to a first particularly preferred embodiment, the solidunsaturated diene elastomer is an isoprene elastomer. Isoprene elastomeris understood to mean an isoprene homopolymer of copolymer, in otherwords an unsaturated diene elastomer selected from the group consistingof natural rubber (NR), synthetic polyisoprenes (IRs),butadiene/isoprene copolymers (BIRs), stirene/isoprene copolymers(SIRs), stirene/butadiene/isoprene copolymers (SBIRs) and the mixturesof these elastomers. Use is more preferably made of natural rubber or asynthetic cis-1,4-polyisoprene, alone or as a blend (mixture) with atleast one other unsaturated diene elastomer as mentioned above, forexample in the form of an NR/BR, NR/SBR, IR/BR or IR/SBR blend, inparticular in the form of an NR/BR blend.

According to another particularly preferred embodiment, the solidunsaturated diene elastomer is a butadiene homopolymer or copolymer,more preferably a butadiene homopolymer, in other words a polybutadiene;preferably, this polybutadiene has a content (mol %) of cis-1,4-bondswhich is greater than 90%, more preferably greater than 95%. It can beused alone or as a blend (mixture) with at least one other unsaturateddiene elastomer as mentioned above.

The above elastomers can, for example, be block, random, sequential ormicrosequential elastomers and can be prepared in dispersion or insolution; they can be coupled and/or star-branched and/or branched oralso functionalized, for example with a coupling and/or star-branchingor functionalization agent. For coupling with carbon black, mention maybe made, for example, of functional groups comprising a C—Sn bond or ofaminated functional groups, such as benzophenone, for example; forcoupling with a reinforcing inorganic filler, such as silica, mentionmay be made, for example, of silanol functional groups or polysiloxanefunctional groups having a silanol end (such as described, for example,in U.S. Pat. No. 6,013,718), of alkoxysilane groups (such as described,for example, in U.S. Pat. No. 5,977,238), of carboxyl groups (such asdescribed, for example, in U.S. Pat. No. 6,815,473 or US 2006/0089445)or of polyether groups (such as described, for example, in U.S. Pat. No.6,503,973). Mention may also be made, as other examples of suchfunctionalized elastomers, of elastomers (such as SBR, BR, NR or IR) ofthe epoxidized type.

The unsaturated diene elastomer of the composition of the invention isby definition solid. In contrast to liquid, solid is understood to meanany substance not having the ability to eventually assume, at the latestafter 24 hours, solely under the effect of gravity and at ambienttemperature (23° C.), the shape of the container in which it is present.

In contrast to elastomers of the liquid type which can optionally beused as liquid plasticizers in the composition of the invention, thissolid unsaturated diene elastomer is characterized by a very highviscosity: its Mooney viscosity in the raw state (i.e., noncrosslinkedstate) ML (1+4), measured at 100° C., is preferably greater than 20,more preferably greater than 30, in particular between 30 and 130.

According to another possible definition, solid elastomer is alsounderstood to mean an elastomer having a high molar mass, that is to saytypically exhibiting a number-average molar mass (Mn) which is greaterthan 100 000 g/mol; preferably, in such a solid elastomer, at least 80%,more preferably at least 90%, of the area of the distribution of themolar masses (measured by SEC) is situated above 100 000 g/mol.

Preferably, the number-average molar mass (Mn) of the unsaturated dieneelastomer is between 100 000 and 5 000 000 g/mol, more preferablybetween 150 000 and 4 000 000 g/mol; in particular, it is between 200000 and 3 000 000 g/mol, more particularly between 200 000 and 1 500 000g/mol. Preferably, its polydispersity index PI (Mw/Mn) is between 1.0and 10.0, in particular between 1.0 and 3.0 as regards a polybutadieneor butadiene copolymer and between 3.0 and 8.0 as regards natural rubberor a synthetic polyisoprene.

A person skilled in the art will know how to adjust, in the light of thepresent description and as a function of the specific applicationtargeted for the composition having a self-sealing property, the averagemolar mass and/or the distribution of the molar masses of the elastomersA and B. According to a specific embodiment of the invention, he can,for example, opt for a broad distribution of molar masses. If he wishesto favour the fluidity of the self-sealing composition, he can insteadfavour the proportion of low molar masses. According to another specificembodiment, which may or may not be combined with the precedingembodiment, he can also favour the proportion of intermediate molarmasses for the purpose of instead optimizing the self-sealing (filling)role of the composition. According to another specific embodiment, hecan instead favour the proportion of high molar masses for the purposeof increasing the mechanical strength of the self-sealing composition.

These various molar mass distributions can be obtained, for example, bycompounding different starting diene elastomers (elastomers A and/orelastomers B).

According to a preferred embodiment of the invention, the above solidunsaturated diene elastomer constitutes the only solid elastomer presentin the self-sealing composition of the invention, that is to say thatthe content of this solid elastomer in the composition is then 100 phr.

According to another specific embodiment of the invention, when it isused as a mixture with other types (other than unsaturated dieneelastomers) of solid elastomers, the above solid unsaturated dieneelastomer preferably constitutes the predominant solid elastomer byweight in the composition of the invention: its content is morepreferably greater than 50 phr, more preferably still greater than 70phr, in particular greater than 80 phr.

Thus, according to specific embodiments of the invention, the solidunsaturated diene elastomer might be combined with other (solid)elastomers which are minor components by weight, whether saturated dieneelastomers (for example butyl elastomers) or elastomers other than dieneelastomers, for example thermoplastic stirene elastomers (referred to as“TPSs”), for example selected from the group consisting ofstirene/butadiene/stirene (SBS), stirene/isoprene/stirene (SIS),stirene/butadiene/isoprene/stirene (SBIS), stirene/isobutylene/stirene(SIBS), stirene/ethylene/butylene/stirene (SEBS),stirene/ethylene/propylene/stirene (SEPS) andstirene/ethylene/ethylene/propylene/stirene (SEEPS) block copolymers,and the mixtures of these copolymers.

Surprisingly, this unsaturated diene elastomer, which is devoid offiller (or with a very low content of filler), has proved to be capable,after addition of a thermoplastic hydrocarbon resin within therecommended narrow range, of fulfilling the function of an effectiveself-sealing composition, as is explained in detail in the continuationof the account.

b) Hydrocarbon Resin

The second essential constituent of the self-sealing composition is ahydrocarbon resin. The designation “resin” is reserved in the presentpatent application, by definition known to a person skilled in the art,for a compound which is solid at ambient temperature (23° C.), incontrast to a liquid plasticizing compound, such as an oil.

Hydrocarbon resins are polymers well known to a person skilled in theart, essentially based on carbon and hydrogen, which can be used inparticular as plasticizing agents or tackifying agents in polymermatrices. They are by nature miscible (i.e., compatible) at the contentsused with the polymer compositions for which they are intended, so as toact as true diluents. They have been described, for example, in the workentitled “Hydrocarbon Resins” by R. Mildenberg, M. Zander and G. Collin(New York, VCH, 1997, ISBN 3-527-28617-9), Chapter 5 of which is devotedto their applications, in particular in the tire rubber field (5.5.“Rubber Tires and Mechanical Goods”). They can be aliphatic,cycloaliphatic, aromatic, hydrogenated aromatic, of thealiphatic/aromatic type, that is to say based on aliphatic and/oraromatic monomers. They can be natural or synthetic and may or may notbe oil-based (if such is the case, they are also known under the name ofpetroleum resins). Their Tg is preferably greater than 0° C., inparticular greater than 20° C. (generally between 30° C. and 95° C.).

In a known way, these hydrocarbon resins can also be described asthermoplastic resins in the sense that they soften on heating and canthus be moulded. They can also be defined by a softening point ortemperature, at which temperature the product, for example in the powderform, sticks together; this datum tends to replace the melting point,which is rather poorly defined, for resins in general. The softeningtemperature of a hydrocarbon resin is generally greater by approximately50 to 60° C. than its Tg value.

In the composition of the invention, the softening temperature of theresin is preferably greater than 40° C. (in particular between 40° C.and 140° C.), more preferably greater than 50° C. (in particular between50° C. and 135° C.).

The said resin is used at a content by weight of between 30 and 90 phr.Below 30 phr, the puncture-resistant performance has proved to beinadequate due to an excessively high stiffness of the composition,whereas, above 90 phr, exposure to an inadequate mechanical strength ofthe material exists with in addition a risk of a damaged performance athigh temperature (typically greater than 70° C.). For these reasons, thecontent of resin is preferably between 40 and 80 phr, more preferablystill at least equal to 45 phr, in particular within a range from 45 to75 phr.

According to a preferred embodiment of the invention, the hydrocarbonresin exhibits at least any one, more preferably all, of the followingcharacteristics:

-   -   a Tg of greater than 25° C.;    -   a softening point of greater than 50° C. (in particular of        between 50° C. and 135° C.);    -   a number-average molecular weight (Mn) of between 400 and 2000        g/mol;    -   a polydispersity index (PI) of less than 3 (reminder: PI=Mw/Mn        with Mw the weight-average molecular weight).

More preferably, this hydrocarbon resin exhibits at least any one, morepreferably all, of the following characteristics:

-   -   a Tg of between 25° C. and 100° C. (in particular between 30° C.        and 90° C.);    -   a softening point of greater than 60° C., in particular of        between 60° C. and 135° C.;    -   an average weight Mn of between 500 and 1500 g/mol;    -   a polydispersity index PI of less than 2.

The softening point is measured according to Standard ISO 4625 (“Ringand Ball” method). The macrostructure (Mw, Mn and PI) is determined bysteric exclusion chromatography (SEC) as indicated in the introductionto the patent application.

Mention may be made, as examples of such hydrocarbon resins, of thoseselected from the group consisting of cyclopentadiene (abbreviated toCPD) or dicyclopentadiene (abbreviated to DCPD) homopolymer or copolymerresins, terpene homopolymer or copolymer resins, terpene/phenolhomopolymer or copolymer resins, C₅ fraction homopolymer or copolymerresins, C₉ fraction homopolymer or copolymer resins, α-methylstirenehomopolymer or copolymer resins, and the mixtures of these resins.Mention may more particularly be made, among the above copolymer resins,of those selected from the group consisting of (D)CPD/vinylaromaticcopolymer resins, (D)CPD/terpene copolymer resins, (D)CPD/C₅ fractioncopolymer resins, (D)CPD/C₉ fraction copolymer resins,terpene/vinylaromatic copolymer resins, terpene/phenol copolymer resins,C₅ fraction/vinylaromatic copolymer resins, and the mixtures of theseresins.

The term “terpene” combines here, in a known way, α-pinene, β-pinene andlimonene monomers; use is preferably made of a limonene monomer, acompound which exists, in a known way, in the form of three possibleisomers: L-limonene (laevorotatory enantiomer), D-limonene(dextrorotatory enantiomer) or else dipentene, the racemate of thedextrorotatory and laevorotatory enantiomers. Suitable as vinylaromaticmonomer are, for example, stirene, α-methylstirene, ortho-methylstirene,meta-methylstirene, para-methylstirene, vinyltoluene,para-(tert-butyl)stirene, methoxystirenes, chlorostirenes,hydroxystirenes, vinylmesitylene, divinylbenzene, vinylnaphthalene orany vinylaromatic monomer resulting from a C₉ fraction (or moregenerally from a C₈ to C₁₀ fraction).

More particularly, mention may be made of the resins selected from thegroup consisting of (D)CPD homopolymer resins, (D)CPD/stirene copolymerresins, polylimonene resins, limonene/stirene copolymer resins,limonene/D(CPD) copolymer resins, C₅ fraction/stirene copolymer resins,C₅ fraction/C₉ fraction copolymer resins, and the mixtures of theseresins.

All the above resins are well known to a person skilled in the art andare commercially available, for example sold by DRT under the name“Dercolyte” as regards the polylimonene resins, by Neville ChemicalCompany under the name “Super Nevtac”, by Kolon under the name “Hikorez”or by Exxon Mobil under the name “Escorez” as regards the C₅fraction/stirene resins or C₅ fraction/C₉ fraction resins, or byStruktol under the name “40 MS” or “40 NS” (mixtures of aromatic and/oraliphatic resins).

c) Crosslinking Agent

The composition prepared according to the process of the invention hasin addition the essential characteristic of comprising, as crosslinkingagent for the solid unsaturated diene elastomer, between 0.5 and 15 phrof thiuram polysulphide.

After curing, such a crosslinking agent has proved to contributesufficient cohesion to the composition, without conferring truecrosslinking thereon: the crosslinking which can be measured, via aconventional inflation method known to a person skilled in the art, isin fact close to the detection threshold. Preferably, the content ofthiuram polysulphide is between 0.5 and 10 phr, more preferably within arange from 1 to 5 phr.

It should be remembered that thiuram polysulphides, known as sulphurdonors and vulcanization accelerators, have the formula (I):

in which:

-   -   x is a number (integer, or decimal number in the case of        mixtures of polysulphides) which is equal to or greater than        two, preferably within a range from 2 to 8;    -   R₁ and R₂, which are identical or different, represent a        hydrocarbon radical preferably chosen from alkyls having from 1        to 6 carbon atoms, cycloalkyls having from 5 to 7 carbon atoms,        or aryls, aralkyls or alkaryls having from 6 to 10 carbon atoms.

In the above formula (I), R₁ and R₂ might form a divalent hydrocarbonradical comprising from 4 to 7 carbon atoms.

Such thiuram polysulphides are preferably selected from the groupconsisting of tetrabenzylthiuram disulphide (“TBzTD”),tetramethylthiuram disulphide (“TMTD”), dipentamethylenethiuramtetrasulphide (“DPTT”), and the mixtures of such compounds, thesepolysulphides having, it should be remembered, the following expandedformulae:

Preferably, use is made of TBzTD, of formula (I) in which R₁ and R₂represent benzyl and x is equal to 2.

The crosslinking of the solid unsaturated diene elastomer does notrequire, in the composition of the invention, the presence of anothercrosslinking agent, neither sulphur nor other additional vulcanizationagent (sulphur donor, vulcanization activator or accelerator). Thecomposition of the invention can thus advantageously be devoid ofsulphur or of such additional vulcanization agents, or else can compriseonly a very small amount thereof, less than 1 phr, preferably less than0.5 phr, more preferably less than 0.2 phr. According to anotheradvantageous embodiment, the composition of the invention can also bedevoid of zinc or zinc oxide (which are known as vulcanizationactivators), or else comprise only a very small amount thereof, lessthan 1 phr, preferably less than 0.5 phr, more preferably less than 0.2phr.

d) Filler

The composition prepared according to the process of the invention hasthe other characteristic of not comprising a filler or comprising a verysmall amount of filler, that is to say of comprising from 0 to less than30 phr of at least one (that is to say, one or more) such optionalfiller.

Filler is understood here to mean any type of filler, whetherreinforcing (typically having nanometric particles, with aweight-average size preferably of less than 500 nm, in particularbetween 20 and 200 nm) or nonreinforcing or inert (typically havingmicrometric particles, with a weight-average size of greater than 1 μm,for example between 2 and 200 μm).

These reinforcing or nonreinforcing fillers are essentially only presentto give dimensional stability, that is to say a minimum mechanicalstrength, to the final composition. Less thereof is preferably placed inthe composition in proportion as the filler is known to be reinforcingwith respect to an elastomer, in particular a diene elastomer, such asnatural rubber or polybutadiene.

An excessively high amount, in particular of greater than 30 phr, nolonger makes it possible to achieve the minimum required properties offlexibility, deformability and ability to creep. For these reasons, thecomposition of the invention preferably comprises from 0 to less than 20phr, more preferably from 0 to less than 10 phr, of filler.

Mention will in particular be made, as examples of fillers known asreinforcing to a person skilled in the art, of carbon black or of areinforcing inorganic filler, such as silica, or a blend of these twotypes of filler.

All carbon blacks are suitable as carbon blacks, for example, inparticular the blacks conventionally used in tires. Mention will forexample be made, among the latter, of carbon blacks of 300, 600, 700 or900 grade (ASTM) (for example, N326, N330, N347, N375, N683, N772 orN990). Suitable in particular as reinforcing inorganic fillers arehighly dispersible mineral fillers of the silica (SiO₂) type, inparticular precipitated or pyrogenic silicas exhibiting a BET specificsurface of less than 450 m²/g, preferably from 30 to 400 m²/g.

Mention will in particular be made, as examples of fillers known asnonreinforcing or inert to a person skilled in the art, of ashes (i.e.,combustion residues), microparticles of natural calcium carbonates(chalk) or synthetic calcium carbonates, of synthetic silicates ornatural silicates (such as kaolin, talc, mica), or of ground silicas,titanium oxides, aluminas or aluminosilicates. Mention may also be made,as examples of lamellar fillers, of graphite particles. Colouringfillers or fillers coloured, for example, by pigments can advantageouslybe used to colour the composition according to the colour desired.

The physical state under which the filler is provided is not important,whether in the form of a powder, microspheres, granules, beads or anyother appropriate densified form. Of course, filler is also understoodto mean mixtures of different reinforcing and/or nonreinforcing fillers.

A person skilled in the art will be able, in the light of the presentdescription, to adjust the content of filler of the composition of theinvention in order to achieve the property levels desired and to adjustthe formulation to the specific application envisaged.

According to a specific and advantageous embodiment of the invention, ifa reinforcing filler is present in the composition, its content ispreferably less than 5 phr (i.e., between 0 and 5 phr), in particularless than 2 phr (i.e., between 0 and 2 phr). Such contents have provedto be particularly favourable to the manufacturing process for thecomposition of the invention, while providing the latter with anexcellent self-sealing performance. Use is more preferably made of acontent of between 0.5 and 2 phr, in particular when carbon black isconcerned.

e) Liquid Plasticizer

Any liquid elastomer or any extending oil, whether of aromatic ornonaromatic nature, more generally any liquid plasticizing agent knownfor its plasticizing properties with respect to elastomers, inparticular diene elastomers, can be used. At ambient temperature (23°C.), these plasticizers or these oils, which are more or less viscous,are liquids, in contrast in particular to hydrocarbon resins, which areby nature solid at ambient temperature.

To recapitulate, in contrast to a solid, liquid is understood to meanany substance having the ability to eventually assume, at the latestafter 24 hours, solely under the effect of gravity and at ambienttemperature (23° C.), the shape of the container in which it is present.

In contrast to solid elastomers, liquid plasticizers and elastomers(i.e., having a low molar mass) are characterized by a very lowviscosity: preferably, their Brookfield viscosity, measured at 65° C.,is less than 2 000 000 cP (cP meaning centipoise; 1 cP is equal to 1mPa·s), more preferably less than 1 500 000 cP; it is in particularbetween 200 and 1 000 000 cP, typically, as regards liquid elastomers,between 2000 and 1 000 000 cP).

According to another possible definition, liquid elastomer is alsounderstood to mean an elastomer for which the number-average molar mass(Mn) is less than 100 000 g/mol; preferably, in such a liquid elastomer,at least 80% and more preferably at least 90% of the area of thedistribution of the molar masses (measured by SEC) is situated below 100000 g/mol.

Suitable in particular are liquid elastomers for which thenumber-average molar mass (Mn) is between 400 and 90 000 g/mol, moregenerally between 800 and 90 000 g/mol, for example in the form ofliquid BR, liquid SBR, liquid IR or liquid depolymerized natural rubber,such as are described, for example, in the abovementioned patentdocuments U.S. Pat. No. 4,913,209, U.S. Pat. No. 5,085,942 and U.S. Pat.No. 5,295,525. If a liquid diene elastomer (for example liquid NR,liquid IR or liquid BR) is used as plasticizer, it can optionally begenerated in situ, that is to say during the actual manufacture of thecomposition of the invention, for example by an appropriate(thermo)mechanical working (depolymerization by chain breakage) of thestarting solid elastomer(s). Use may also be made of mixtures of suchliquid elastomers with oils, such as described below.

Extending oils, in particular those selected from the group consistingof polyolefin oils (that is to say, resulting from the polymerization ofolefins, monoolefins or diolefins, for example of the polyethyleneglycol or polypropylene glycol type), paraffinic oils, naphthenic oils(of low or high viscosity and hydrogenated or nonhydrogenated), aromaticor DAE (Distillate Aromatic Extracts) oils, MES (Medium ExtractedSolvates) oils, TDAE (Treated Distillate Aromatic Extracts) oils,mineral oils, vegetable oils (and their oligomers, e.g., palm, rapeseed,soybean or sunflower oils) and the mixtures of these oils, are alsosuitable.

According to a specific embodiment, use is made, for example, of an oilof the polybutene type, in particular a polyisobutylene (abbreviated to“PIB”) oil, which has demonstrated an excellent compromise in propertiesin comparison with the other oils tested, in particular with aconventional oil of the paraffinic type. By way of examples, PIB oilsare sold in particular by Univar under the name “Dynapak Poly” (e.g.“Dynapak Poly 190”) and by BASF under the “Glissopal” (e.g. “Glissopal1000”) or “Oppanol” (e.g. “Oppanol B12”) names; paraffinic oils aresold, for example, by Exxon under the name “Telura 618” or by Repsolunder the name “Extensol 51”.

Also suitable as liquid plasticizers are ether, ester, phosphate orsulphonate plasticizers, more particularly those selected from estersand phosphates. Mention may be made, as preferred phosphateplasticizers, of those which comprise between 12 and 30 carbon atoms,for example trioctyl phosphate. Mention may in particular be made, aspreferred ester plasticizers, of the compounds selected from the groupconsisting of trimellitates, pyromellitates, phthalates,1,2-cyclohexanedicarboxylates, adipates, azelates, sebacates, glyceroltriesters and the mixtures of these compounds. Mention may be made,among the above triesters, as preferred glycerol triesters, of thosewhich are composed predominantly (for more than 50% by weight, morepreferably for more than 80% by weight) of an unsaturated C₁₈ fattyacid, that is to say a fatty acid selected from the group consisting ofoleic acid, linoleic acid, linolenic acid and the mixtures of theseacids. More preferably, whether of synthetic or natural origin (thecase, for example, of sunflower or rapeseed vegetable oils), the fattyacid used is composed, for more than 50% by weight, more preferablystill for more than 80% by weight, of oleic acid. Such triesters(trioleates) having a high content of oleic acid are well known—theyhave been described, for example, in Application WO 02/088238 (or US2004/0127617)—as plasticizing agents in tire treads.

The number-average molar mass (Mn) of the abovementioned liquidplasticizers other than liquid elastomers is preferably between 400 and25 000 g/mol, more preferably still between 800 and 10 000 g/mol(measured by SEC, as indicated above for the hydrocarbon resin). Forexcessively low Mn masses, there can exist a risk of migration of theplasticizer to the outside of the composition, whereas excessively highmasses can result in excessive stiffening of the composition. An Mn massof between 1000 and 4000 g/mol has proved to constitute an excellentcompromise for the targeted applications, in particular for use in atire.

To sum up, the liquid plasticizer is preferably selected from the groupconsisting of liquid elastomers, polyolefin oils, naphthenic oils,paraffinic oils, DAE oils, MES oils, TDAE oils, mineral oils, vegetableoils, ether plasticizers, ester plasticizers, phosphate plasticizers,sulphonate plasticizers and the mixtures of these compounds. Morepreferably, this liquid plasticizer is selected from the groupconsisting of liquid elastomers, polyolefin oils, vegetable oils and themixtures of these compounds.

A person skilled in the art will be able, in the light of thedescription and implementational examples which follow, to adjust theamount of liquid plasticizer as a function of the nature of the latterand of the specific conditions of use of the self-sealing composition,in particular of the inflatable article in which it is intended to beused.

Preferably, the content of liquid plasticizer is within a range from 5to 40 phr, more preferably within a range from 10 to 30 phr. Below theminima indicated, there is a risk of the elastomer compositionexhibiting a stiffness which is too high for some applications, whereas,above the recommended maxima, a risk arises of insufficient cohesion ofthe composition and of a deterioration in the self-sealing properties.

f) Other Possible Additives

Various other additives can be added, typically in a small amount(preferably at contents of less than 20 phr, more preferably of lessthan 15 phr), such as, for example, protection agents, such as UVstabilizers, antioxidants or antiozonants, various other stabilizers, orcolouring agents which can advantageously be used for the colouring ofthe self-sealing composition. According to the application targeted,fibres, in the form of short fibres or of a slurry, might optionally beadded to give greater cohesion to the self-sealing composition. Inaddition to the elastomers described above, the self-sealing compositionmight also comprise, still according to a fraction by weight which ispreferably a minor fraction with respect to the unsaturated dieneelastomer, polymers other than elastomers, such as, for example,thermoplastic polymers.

II. IMPLEMENTATIONAL EXAMPLE OF THE INVENTION

II-1. Manufacture of the Self-Sealing Composition

By way of example, the stage (a) of manufacture of the masterbatch ispreferably carried out in a compounding screw extruder as representeddiagrammatically in a simple way in FIG. 1.

This FIG. 1 shows an example of a compounding screw extruder (10)essentially comprising an extrusion screw (for example a single screw)(11), a first metering pump (12) for the unsaturated diene elastomer(solid) and a second metering pump (13) for the resin (solid or liquid)and optionally the liquid plasticizer. The hydrocarbon resin and theoptional liquid plasticizer can be introduced by means of a singlemetering pump, if they have already been mixed beforehand, or else canbe introduced separately by means of two separate metering pumps (justone represented in FIG. 1). The metering pumps (12, 13) make it possibleto increase in pressure while retaining control of the metering and theinitial characteristics of the materials, the separation of the metering(elastomer and resin) and compounding functions in addition offeringbetter control of the process.

The products, pushed by the extrusion screw, are intimately mixed underthe very strong shearing contributed by the rotation of the screw, thusprogressing through the mixer, for example up to a “chopper-homogenizer”part (14), at the outlet of which zone the final masterbatch (15) thusobtained, progressing in the direction of the arrow (F), is finallyextruded through a die (16) which makes it possible to extrude theproduct at the desired dimensions. According to a specific embodiment,it can be advantageous to maintain the “chopper-homogenizer” part at alower temperature than that of the extrusion screw, for example at atemperature of between 40° C. and 60° C., this being done in order tolimit the adhesiveness of the masterbatch and thus to improve themechanical working and the homogeneity of the masterbatch.

By way of example, the masterbatch thus extruded, which is ready to beused, can be subsequently transferred and cooled, for example on anexternal mixer of the two-roll open mill type, for introduction of thecrosslinking agent and of the optional filler; the temperature insidethe said external mixer of the two-roll open mill type is preferablykept lower than the softening temperature of the resin, furthermorepreferably lower than 100° C., in particular lower than 80° C.Advantageously, the above rolls are cooled, for example by circulationof water, to a temperature of less than 40° C., preferably of less than30° C., so as to prevent or limit undesirable adhesive bonding of thecomposition to the walls of the mixer.

It is possible to directly form the masterbatch at the outlet of theextrusion device (10) in order to make it easier to transport it and/orto place it on the external mixer. It is also possible to use continuousfeeding of the external mixer of the two-roll open mill type.

By virtue of the preferred specific device and preferred processdescribed above, it is possible to prepare the composition of theinvention under satisfactory industrial conditions, without the risk ofcontaminating the equipment due to excessive undesirable adhesivebonding of the composition to the walls of the mixers.

II-2. Use of the Self-Sealing Composition as Puncture-Resistant Layer

The self-sealing composition prepared according to the process of theinvention is a solid compound which is characterized in particular, byvirtue of its specific formulation, by very great flexibility and highdeformability. Its Mooney viscosity, measured at 35° C. in the raw state(i.e., before curing), is preferably greater than 20, more preferablybetween 20 and 80, according to its specific formulation and theapplication targeted, in particular according to the presence or absenceof a liquid plasticizing agent.

It can be used as puncture-resistant layer in any type of “inflatable”article, that is to say, by definition, any article which takes itsusable form when inflated with air. Mention may be made, as examples ofsuch inflatable articles, of inflatable boats, or balls used for play orsport.

is It is particularly well suited to use as puncture-resistant layer inan inflatable article, a finished or semi-finished product, made ofrubber, in particular in tires for a motor vehicle, such as a vehicle ofthe two-wheel, passenger or industrial type, or a vehicle other than amotor vehicle, such as a bicycle, more particularly in tires forpassenger vehicles capable of running at very high speed or tires forindustrial vehicles, such as heavy duty vehicles, capable of running andoperating under particularly high internal temperature conditions.

Such a puncture-resistant layer is preferably positioned on the internalwall of the inflatable article, completely or least partially coveringit, but it can also be completely incorporated into its internalstructure.

The self-sealing composition described herein has the advantage ofexhibiting, within a very wide range of operating temperatures for thetires, virtually no disadvantage in terms of rolling resistance incomparison with a tire not comprising a self-sealing layer. Incomparison with normal self-sealing compositions, the risks of excessivecreep during use at relatively high temperature (typically greater than60° C.), a temperature frequently encountered during the use of sometires, are notably reduced. Its self-sealing properties are alsoimproved during use at low temperature (typically less than 0° C.), inparticular when the solid unsaturated diene elastomer comprises amixture of natural rubber and polybutadiene.

By way of example, the appended FIG. 2 represents, highly schematically(without observing a specific scale), a radial cross section of a tirein accordance with the invention.

This tire 20 comprises a crown 21 reinforced by a crown reinforcement orbelt 25, two sidewalls 22 and two beads 23, each of these beads 23 beingreinforced with a bead wire 24. The crown 21 is surmounted by a tread,not represented in this schematic figure. A carcass reinforcement 26 iswound around the two bead wires 24 in each bead 23, the turn-up 27 ofthis reinforcement 26 being, for example, positioned towards the outsideof the tire 20, which is here represented fitted to its wheel rim 28.The carcass reinforcement 26 is, in a way known per se, composed of atleast one ply reinforced by cables, known as “radial” cables, forexample of textile or metal, that is to say that these cables arepositioned virtually parallel to one another and extend from one bead tothe other so as to form an angle of between 80° and 90° with the mediancircumferential plane (plane perpendicular to the axis of rotation ofthe tire which is situated at mid-distance from the two beads 23 andpasses through the middle of the crown reinforcement 25).

The tire 20 is characterized in that its internal wall comprises amultilayer laminate (30) comprising at least two layers (30 a, 30 b),which is self-sealing by virtue of its first layer (30 a) and airtightby virtue of its second layer (30 b), for example based on butyl rubber.The two layers (30 a, 30 b) cover substantially the entire internal wallof the tire, extending from one sidewall to the other, at least as faras the level of the rim flange when the tire is in the fitted position.The laminate is positioned here in such a way that the firstself-sealing layer (30 a) is radially the innermost in the tire, withrespect to the other layer (30 b). In other words, the self-sealinglayer (30 a) covers the airtight layer (30 b) on the side of theinternal cavity 29 of the tire 20.

In this example, the layer 30 b (with a thickness of 0.7 to 0.8 mm) isbased on butyl rubber and exhibits a conventional formulation for aninner liner, which normally defines, in a conventional tire, theradially internal face of the said tire intended to protect the carcassreinforcement from the diffusion of air originating from the spaceinterior to the tire. This airtight layer 30 b thus makes it possible toinflate the tire 20 and to keep it pressurized; its airtightnessproperties allow it to guarantee a relatively low rate of loss ofpressure, making it possible to keep the tire inflated, in a normaloperating state, for a sufficient period of time, normally several weeksor several months.

The layer 30 a is, for its part, composed of a self-sealing compositionprepared according to the process in accordance with the inventioncomprising, in this example, a solid unsaturated diene elastomer (blendof 50 phr of solid NR with 50 phr of solid BR; number-average molar massMn of the blend of elastomers equal to approximately 270 000 g/mol inthe final composition); a hydrocarbon resin “Escorez 2I01” from ExxonMobil (Tg equal to approximately 44° C.; softening point equal toapproximately 90° C.; Mn equal to approximately 800 g/mol; PI equal toapproximately 2.1) at a content by weight of approximately 50 phr;approximately 15 phr of liquid polybutadiene elastomer (“Ricon 154” fromSartomer Cray Valley—Tg equal to approximately −20° C.; Mn equal toapproximately 5000 g/mol and PI equal to approximately 1.4); and 3 phrof TBzTD; in addition, it comprises a very small amount (approximately 1phr) of carbon black (N772) and approximately 3 phr of antioxidant.

The Mooney viscosity ML (1+4) at 100° C. of the two starting elastomers,BR and NR, is respectively equal to approximately 45 and approximately85. For each of the two elastomers, more than 80% of the area of thedistribution of the molar masses (measured by SEC) is situated above 100000 g/mol.

The above self-sealing composition was prepared using a single-screwextruder (LID=40), such as represented diagrammatically in FIG. 1(already commented on above); the mixing of the base constituents (BR,NR, resin) was carried out at a temperature (of between 100 and 130° C.)greater than the softening temperature of the resin. The extruder usedcomprised three different feeds (hoppers) (BR, NR, resin) and a pump forliquid injection under pressure for the resin (injected at a temperatureof 100 to 110° C. approximately); when the elastomers and the resin arethus intimately mixed, it was found that the undesirable adhesiveness ofthe composition very significantly decreased.

The above extruder was provided with a die which makes it possible toextrude the masterbatch at the desired dimensions (for example in theform of a strip) into an external mixer of the two-roll open mill type,for final incorporation of the other constituents, namely thecrosslinking agent (TBzTD), carbon black and antioxidant, at lowtemperature kept at a value of less than +30° C. (cooling the rolls bycirculation of water). Finally, the liquid plasticizer was introducedduring a stage (c), after the stage (b) of incorporation of thecrosslinking agent (all of it, i.e. 3 phr in this example) on anexternal mixer of the two-roll open mill type; this stage (c) wascarried out at a temperature of between 80° C. and 130° C., by passingand mixing through a compounding screw extruder of the same type as thatused in stage (a).

The layer 30 a, positioned, for example, in FIG. 2, between the layer 30b and the cavity 29 of the tire of FIG. 2, makes it possible to providethe tire with effective protection against pressure losses due toaccidental perforations, by making possible the automatic sealing ofthese perforations.

During trials, tires of passenger vehicle type, of 205/55 R16 size,“Michelin, Energy 3 brand”, were tested. The internal wall of the tires(already comprising the airtight layer (30 b) was covered with theself-sealing layer (30 a) described above, with a thickness of 3 mm, andthen the tires were vulcanized.

Four perforations with a diameter of 5 mm were produced on one of thefitted and inflated tires, through the tread and the crown block, usingpunches which were immediately removed.

Unexpectedly, this tire withstood being run on a rolling drum at 150km/h, under a nominal load of 400 kg, without loss in pressure for morethan 1500 km, after which distance running was halted.

Without a self-sealing composition and under the same conditions asabove, the tire thus perforated loses its pressure in less than aminute, becoming completely unsuitable for running.

The invention claimed is:
 1. A process for the manufacture of aninflatable article, wherein the inflatable article has an internal wall,the internal wall comprises a puncture-resistant layer formed of anelastomer composition which has a self-sealing property and comprises: asolid unsaturated diene elastomer; between 30 and 90 phr of ahydrocarbon resin; a total amount of between 0 phr and 10 phr filler;between 0.5 and 15 phr of thiuram polysulphide, wherein the processcomprises: 1) preparing the elastomeric composition; and 2)incorporating the elastomeric composition into the inner wall of theinflatable article; the step 1) comprises, during a stage (a), preparinga masterbatch comprising at least the solid unsaturated diene elastomerand the hydrocarbon resin is by mixing at least the solid unsaturateddiene elastomer and the hydrocarbon in a mixer at a temperature which isgreater than the softening temperature of the hydrocarbon resin.
 2. Theprocess according to claim 1, wherein, during the stage (a), the solidunsaturated diene elastomer is brought into contact with the hydrocarbonresin in the solid state.
 3. The process according to claim 1, wherein,during the stage (a), the solid unsaturated diene elastomer is broughtinto contact with the hydrocarbon resin in the liquid state.
 4. Theprocess according to claim 3, wherein the hydrocarbon resin is injectedin the liquid state into the mixer.
 5. The process according to claim 1,wherein the temperature is greater than 70° C.
 6. The process accordingto claim 1, wherein the stage (a) is carried out in a compounding screwextruder.
 7. The process according to claim 1, wherein, during a stage(b), the thiuram polysulphide is incorporated in the masterbatchprepared in the stage (a).
 8. The process according to claim 7, whereinthe stage (b) is carried out in a compounding screw extruder.
 9. Theprocess according to claim 7, wherein the stage (b) is carried out on anexternal mixer of the two-roll open mill type.
 10. The process accordingto claim 7, wherein the temperature during the stage (b) is kept lowerthan the softening temperature of the hydrocarbon resin.
 11. The processaccording to claim 7, wherein the temperature during the stage (b) iskept lower than 130° C.
 12. The process according to claim 11, whereinthe temperature during the stage (b) is kept lower than 50° C.
 13. Theprocess according to claim 7, wherein an intermediate stage of coolingthe masterbatch is inserted between said stages (a) and (b) in order tocool the masterbatch to a temperature lower than the softeningtemperature of the hydrocarbon resin.
 14. The process according to claim7, wherein an intermediate stage of cooling the masterbatch is insertedbetween said stages (a) and (b) in order to cool the masterbatch to atemperature lower than 130° C.
 15. The process according to claim 7,wherein a liquid plasticizer having a glass transition temperature (Tg)of less than −20° C. is additionally incorporated during the stage (b).16. The process according to claim 7, wherein a liquid plasticizerhaving a glass transition temperature (Tg) of less than −20° C. isincorporated during a stage (c) subsequent to the stage (b) in the samemixer or a different mixer from that of the stage (b).
 17. The processaccording to claim 16, wherein the stage (c) is carried out in acompounding screw extruder.
 18. The process according to claim 16,wherein the stage (c) is carried out on an external mixer of thetwo-roll open mill type.
 19. The process according to claim 1, whereinthe solid unsaturated diene elastomer is selected from the groupconsisting of polybutadienes, natural rubber, synthetic polyisoprenes,butadiene copolymers, and mixtures of such elastomers.
 20. The processaccording to claim 19, wherein the solid unsaturated diene elastomer isnatural rubber, a polybutadiene, or a mixture of natural rubber andpolybutadiene.
 21. The process according to claim 1, wherein the contentof the solid unsaturated diene elastomer is greater than 50 phr.
 22. Theprocess according to claim 1, wherein the solid unsaturated dieneelastomer constitutes the only solid elastomer of the composition. 23.The process according to claim 1, wherein the number-average molar massMn of the solid unsaturated diene elastomer is between 100,000 and5,000,000 g/mol.
 24. The process according to claim 1, wherein thecontent of hydrocarbon resin is within a range from 45 to 75 phr. 25.The process according to claim 1, wherein the hydrocarbon resin exhibitsa glass transition temperature (Tg) of greater than 0° C.
 26. Theprocess according to claim 1, wherein the number-average molar molecularweight Mn of the hydrocarbon resin is between 400 and 2000 g/mol. 27.The process according to claim 1, wherein the hydrocarbon resin isselected from the group consisting of cyclopentadiene (CPD) homopolymeror copolymer resins, dicyclopentadiene (DCPD) homopolymer or copolymerresins, terpene homopolymer or copolymer resins, terpene phenolhomopolymer or copolymer resins, C₅ fraction homopolymer or copolymerresins, C₉ fraction homopolymer or copolymer resins, α-methylstyrenehomopolymer or copolymer resins, and mixtures thereof.
 28. The processaccording to claim 1, wherein the filler is introduced during a stagesubsequent to stage (a).
 29. The process according to claim 1, whereinthe filler consists of carbon black.
 30. The process according to claim29, wherein the content of the filler is less than 5 phr.
 31. Theprocess according to claim 30, wherein the content of the filler isbetween 0.5 and 2 phr.
 32. The process according to claim 1, wherein thecontent of thiuram polysulphide is between 1 and 10 phr.
 33. The processaccording to claim 1, wherein a liquid plasticizer having a glasstransition temperature (Tg) of less than −20° C. is additionallyincorporated in the composition.
 34. The process according to claim 33,wherein the content of liquid plasticizer is less than 60 phr.
 35. Theprocess according to claim 34, wherein the content of liquid plasticizeris within a range from 5 to 40 phr.
 36. The process according to claim33, wherein the liquid plasticizer is selected from the group consistingof liquid elastomers, polyolefin oils, naphthenic oils, paraffinic oils,DAE oils, MES oils, TDAE oils, mineral oils, vegetable oils, etherplasticizers, ester plasticizers, phosphate plasticizers, sulphonateplasticizers, and mixtures thereof.
 37. The process according to claim36, wherein the liquid plasticizer is selected from the group consistingof liquid elastomers, polyolefin oils, vegetable oils, and mixturesthereof.
 38. The process according to claim 33, wherein thenumber-average molar mass Mn of the liquid plasticizer is between 400and 90,000 g/mol.
 39. The process according to claim 33, wherein theliquid plasticizer is incorporated in the masterbatch during stage (a).